Fluorescent lamp



Feb. 11,1964 c. E. SWANSON FLUORESCENT LAMP 2 Sheets-Sheet 1 Filed Aug. 31', 1960 INVENTOR. 042/. E. .SWAA/sm/ By 091%, #9111 Feb. 11, 1964 'c. s. SWANSON FLUORESCENT LAMP 2 Sheets-Sheet 2 Filed Aug. 31, 1.960

United States Patent 3,121,183 FLUGRESQENT LANE Carl E. Swanson, North Arlington, NJ assignor to Darolfest Qorporation, North Eergen, Ni, a corporation of New York Filed Aug. 31, 192%), Set. N 53,077 18 Qiaims. (U. 3l32tl4) This invention relates to electric discharge lamps and more particularly to electric larnps of the fluorescent type having an elongated tubular envelope in which the path of the arc-stream is controlled.

Many types of low pressure discharge lamps are currently in use today. One common type is the fluorescent lamp, which is a low pressure, positive column type of lamp having the general shape of an elongated tubular envelope. The inside or" the envelope has a phosphor coating which is excited to produce light in the visible frequency range by the resonance radiation of an atom of a particular type of material. In the typical fluorescent lamp, mercury is utilized to provide the atoms which emit the resonance radiation. Visible light is produced by first vaporizing the mercury and forming a plasma containing mercury atoms. When an electron collides with a mercury atom in the plasma the atom is raised to the first excited state. In going back to the normal state the atom emits a quantum of energy having a wavelength which is dependout upon the energy lost in going from the first excited state back to the normal state. In the case of mercury atoms, the emitted energy has a wavelength of 2537 Angstroms. The emitted energy reacts with the phosphor on the inside of the lamp to produce light of a visible nature. The phenomena occurring in this type of lamp are well known and other lamps have also been constructed using not onlf, mercury but other materials, for example, sodium, which emit radiation of different wavelengths.

In general, lamp lumen output is proportional to lamp current loading so that a lamp of a given length has a higher lumen output for a given current loading than a lamp of the same length which has a lower current loading. It is therefore desirable to construct fluorescent lmps so that they will be able to withstand higher current loadings thereby giving a greater efl'lciency for each lamp. When this is done, a greater lumen output can be obtained with fewer lamps operating at the high current loadings.

In accordance with the present invention, in order to increase the current loading of a fluorescent lamp so that it can operate at higher than normal current loading thereby obtaining higher lumen output, means are provided on the inside of the tubular lamp envelope to modify the arcstream. The arc-stream path-modifying means changes the path of the arc-stream on the inside of the tube so as to provide one or more of the following conditions: (1) more surface area of phosphor exposed to the arcstream; (2) an arc-stream length longer than the length of the lamp; and (3) a cross-sectional area for the lamp which generally squeezes the cross-section of the arcstream into an ova shape so that the eifective electron temperature of the plasma is increased, and the loss due to imprisonment of resonance radiation is reduced because of the close proximity of the arc-stream to a wall. The use of the internal arc-stream path-modifying means not only increases the eficiency of the lamp but also allows the production of lamps having modified arc-streams in which the standard circular outer tube and its inherent advantages of easy manufacture and high structural strength are retained.

It is therefore an object of this invention to provide a fluorescent lamp having increased eficiency.

Another object of this invention is to provide a lamp having arc-stream path-modifying means.

It is a further object of this invention to provide a fluorescent lamp in which arc-stream path-modifying plates are provided on the inside of the lamp envelope.

Still another object of this invention is to provide a fluorescent lamp having helical arc-stream path-modifying plates.

Other objects and advantages of the present invention will become more apparent upon reference to the following specification and annexed drawings in which:

FIGURE 1 is a perspective view partially broken away of a lamp made according to the invention;

FIGURE 2 is a cross-section of the lamp taken along lines 22 of FIGURE 1;

FIGURE 3 is a cross-section of the lamp taken along lines 33 of FIGURE 1;

FIGURE 4 is a cross-section of another embodiment of a lamp having difierent shaped arc-stream modifying plates;

FIGURE 5 is a perspective View of another embodiment f the invention in which the arc-stream modifying plates are formed in a spiral;

FIGURE 6 is a perspective view of another embodiment of arc-stream modifying plates; and

FIGURE 7 is a perspective view of still another embodiment of arc-stream modifying plates.

It is generally understood in the present state of the art that an increase in the eifective electron temperature of the plasma in a fluorescent lamp results in a more efficient production of excited atoms. This allows the addition of more energy per foot of arc without a decrease in the ei ciency of light production. Several factors contribute to the increase of effective electron temperature. These factors include: a relative reduction in the wattage loss in the lamp electrodes by increasing the length of the arc-stream; a modification of the cross-section of the are into a non-circular shape which decreases the loss of energy due to imprisonment of resonance radiation; and, an increase in the mobility of the mercury ions in the plasma brought about by the use of neon or helium as a part of the fill gas mixture in the lamp along with the normal argon starting gas. It is also known that by providin the lamp with one or more cool zones, which are zones of relatively low temperature (approximately 40 degrees centigrade), a limit is placed on the mercury pressure of the operating lamp at between 6-10 microns. This pressure represents that pressure at which maximum ultraviolet radiation is produced. Specifically, a lamp operating at 1.5 of fill gas pressure and at a mercury pressure of approximately 7 microns has a discharge are with a major dimension that can be spread to approximately three times the minor dimension. This spread produces a substantially oval shaped are which increases the eifective electron temperature.

Several attempts have been made in prior art lamps to modify the arc-stream path. In the prior art lamps portions of the outer bulb are deformed to have noncircular cross-sections. In one such type of lamp, the non-circular cross-sectional areas are formed in a crene lated pattern thereby providing a wavy and somewhat longer path for the arc-stream. In general, lamps having non-circular tube cross-sections have several features which are sometimes considered to be disadvantageous. Among these features are that the tubes must be formed by special processes in order to achieve the non-circular cross-sections and the tubes so formed are somewhat structurally Weaker so that handling must be done in a relatively careful manner. All of these disadvantageous features are overcome by the present invention.

Referring to FIGURE 1, the fluorescent lamp has an outer tube 11 of substantially cylindrical shape which is made of a suitable transpare t "treous material such as glass or quartz. The tube shouldered down at the ends 13 in order to accommodate a respective base connector l5. Connector 15 has at the end thereof a contact member 17 which holds the lamp into a fixture (not shown) to make electrical contact with the external current source and ballast (not shown A stem 19, through which lead-in Wires 21 from the contact 17 are brought into the tube is sealed into each end of the tube 11. Each lead-in wire 21 is brought out through a ceramic tube 22 which is cemented to the top of a stem 19. A filament-cathode 23, which may be of the conventional triple-coiled type, is connected between two lead-in wires 21 for a source of electrons for the arc discharge. A tubulation (not shown) is formed at one or both ends or the tube 11, usually as a part of the stem 1h, through which the inside of the tube 11 is exhausted and then filled with the starting gas and the fill-gas mixture to the desired pressures. The desired amount of mercury (not shown) is also introduced into the tube.

A heat-shield 25, in the form or" a disk of nickel, is placed behind the filament cathode 23 at each end of the lamp. The heat shield 25 is electrically connected to one of the lead-in wires and insulated from the other lead-in wire passing through a respective stem 19. The heat shields 25 create the major coo-ling zones for the lamp at the respective ends of the lamp. The cooling zones limit the mercury pressure so that maximum ultraviolet radiation output is maintained.

A pair of arc-stream modifying plates 3% and 31 are provided which are spaced substantially parallel with respect to each other and run the length of the tube 11 between the heat shields 25. The plates 3t? and 31 are made of a suitable transparent material such as glass, quartz or vicor and are held against the inner wall of the tube ll by a spring 33 at each end of the tube (see FIGURE 2). If desired, the plates 3t? and 31 may be fused or cemented to the inner wall of the tube 12. As shown in the crosssections of FIGURES 2 and 3, the plates 39 and 31 are flat and are cut to have a width to form a substantially rectangular cross-sectional area therebetween. Typical dimensions for the plates 30 and 31 in a T12 bulb (twelve /8 inch units of diameter) are selected to form an inner cross-sectional area of approximately 1% inches along dimension b by of an inch along dimension 0. For a T17 bulb, with an outside diameter of 2% inches, the respective dimensions b and c would be 2 inches by 1 inch. It should be realized, that these dimensions may be varied in accordance with the results desired and the type of tube used.

The inner surface of the transparent plates 3! and 31 have deposited thereon a phosphor coating 35, which may be any desired phosphor compound or mixture, many of which are well known in the art. The phosphor coating 35 is also deposited on the inner surface of the tube 11 between the two plates thereby completely coating the inner surface of the perimeter formed by the plates 3% and 3d and the inner tube wall therebetween. The portions of the tube ll opposite the two plates 34 an 31 are left uncoated so that the light produced by the phosphor coating on the plates may be radiated outwardly from the bulb. The portions of the tube between the heat shields 25 and the tube ends are completely coated in the normal manner.

As shown in FEGURE 3, due to the use of the two plates 31; and 31 the arc-stream is compressed into a substantially oval shape, as shown by the lines 4%. As discussed above, the oval cross-sectional area for the arcstream raises the effective electron temperature of the plasma thereby increasing the efficiency or" the lamp.

in order to increase the efiiciency of the lamp, the plates may be curved, as the plates 43 and 44 of FIG- URE 4, thereby increasing the amount of phosphor surface exposed to the arc stream. The curved plates 4-3 and x i4 are mounted inside of the tube 11, in the manner described with respect to the tes and 31 of FIGURES l3, so that they are spaced substantially parallel to each other along the length or" the tube between the heat shields 25. As before, phosphor is coated on the inner surface of the plates and on the inner wall of the tube Ill in V posed to the arc-stream as in a circular walled tube, but

the more effective arc-stream cross section is obtained thereby increasing the lamp efficiency.

in order to improve light distribution the flat plates of the lamp of FiGURES 1-3 or the curved plates of the lamp of FIGURE 4 are formed in a spiral or helix as shown by the plates and 51 of FIGURE 5. The geometric form that each plate describes can be called a helicoid. The slices for the plates 5b and 51 may be made with any desired pitch with a higher pitch giving more uniform lamp surface area. Cross-sections of the lamp with the helically formed plates 50 and 51 are shown at equal distances d along the tube length. In this embodiment, the plates 5d and 51 are also made of glass, vicor, quartz, or other transparent material and their inner surfaces are coated with the phosphor 35. The portions of the tube 11, which are opposite the spiral plates and El, whether the plates 5% and 51 are fiat or curved, are uncoated, as in FIGURES 1-4, so that the light produced by the phosphor coated on the inside of the plates can radiate through the tube 11.

In the lamp of FEGURE 5, the arc-stream travels in a helical path between the plates 56 and 51. This arrangement also results in a greater uniformity of radiated light.

L1 each of the lamps described in FIGURES 13, 4 and 5, the center of the arc-stream is always in the center of the cross-section of the area formed between the two plates. As pointed out before, when the arc-stream length is longer than the length of the lamp, the eflioiency of the lamp is increased. This may be accomplished by giving the arc-stream a deflection lateral to its direction of travel down the tube 11. This is accomplished by the arc-stream modifying plates 6%? to 61 shown in FIG- URE 6. As can be seen, the upper plate 69 has spaced arcuate indentations 63 extending downward while the bottom plate 61 has upwardly extending arcuate indentation '64 spaced therebetween. Therefore, when the arcstream is traveling between the plates, it is given lateral (up and down between the plates) deflection at the indentations 63 and 6 3- so that it travels a wavy path, which is shown by the line 66 between the two plates. This wavy path increases the length of the arc-stream path thereby improving the efiiciency of the lamp. In addiion, the arc-stream is compressed to have a substantially oval cross-section and the indentations 63 and 64 provide more phosphor surface area to be exposed to the arcstream.

It should be realized that a lamp using plates similar to the plates 6% and 61 may be constructed according to the principles previously described. First of all, the two plates 6% and 61 are placed within the tube 11 and their inner surfaces are coated with phosphor. The portion of the tube opposite the plates is left clear. Further, the plates 69 and 61 may be made flat, as shown, or else they may be formed in the helical pattern in a manner similar to that described with respect to the lamp of FIGURE 5.

FIGURE 7 shows another type of structure which may be used inside the tube 11 in order to increase the arcstream length. In this embodiment, the plates 70 and 71 are crenelated, having alternate long sections 73 and short sections 74 and vertical walls 75 therebetween. The plates 70 and 71 are placed inside of the tube 11 so that the arrangement shown in FIGURE 7 is obtained whereby a short section 74 of plate 70 faces a long section 73 of plate 71 and vice-versa. Therefore, as the arcstream travels between the plates 76 and 71 it has a wavy path.

In the embodiment of FIGURE 7, the inner surfaces of the plates facing each other are coated with phosphor as are the surfaces of the vertical walls 75 which face each other land the portions of the tube wall between the plates. This coating is done and the plates secured to the inside of the tube 11, in the manner previously described. Use of the crenelated structure not only increases the arc-stream length but also increases the amount of phosphor surface area exposed to the arcstream due to the phosphor coating on the inner surfaces of the vertical walls 75. Additionally, the arc-stream is compressed to a substantially oval cross-section between the two plates. All of these factors combine to give a highly efiicient lamp.

The arc-stream path-modifying plates for any of the embodiments of the invention may be made by any standard glass manufacturing techniques such as pressing, molding, twisting, etc. After the plates are formed they are secured to the inside of the tube. The plates may first be coated with phosphor if desired and then inserted into the tube, whose inner surface has ben coated previously in the desired manner to match the shape of the plates. In a preferred embodiment of the invention, the plates are first inserted into a clear tube and secured therein. The phosphor coating is then deposited by the process of raising a column of fluorescent coating material by air pressure to fill the space within the plates and then releasing the column. The phosphor adheres to the exposed surfaces of the plates and the tube wall. in the present case, since the plates form a closed surface on the inner tube wall where they engage it, no phosphor is deposited on the inside of the tube wall in the areas outside that formed by the plates. The ends of the tube, which do not have the plates are coated with phosphor.

After the bulb is coated, it is then dried with a gentle flow of clean air, and baked in a lehr or roller oven to clean out all traces of solvent and lacquer which were part of the fluorescent coating mix. The filament-cathode, base connectors, stems, and other elements are then inserted and both ends of the bulb 11 are then sealed in the standard manner. The lamp is then exhausted in accordance with the accepted procedure and filled with a small amount of mercury and a 'lill gas of either argon, or argon-helium mixture.

While the invention has been described with respect to a standard fluorescent lamp of the mercury type, it should be realized that its principles are not limited thereto. The principles of the invention may be extended to be used with other types of latnps, for example, those using sodium as a radiation emitting material. Other types and shapes of tubes may also be utilized so that, for example, the arc-stream path-modifying plates can be used with a tube having a non-circular cross-section; thereby obtaining the advantages of both structures. It should also be realized that plates having other shapes than those shown may also be utilized.

Therefore it is seen, that a novel fluorescent lamp has been described which has all of the advantages attendant to increasing the arc-stream length, making t e arc-stream cross-section area non-circular, and exposing the maximum amount of phosphor surface area to the arc-strea1n, without modifying the tube itself.

While a preferred embodiment of the invention has been described above it will be understood that this emr 5 bodiment is illustrative only and the invention is to be limited solelyby the appended claims.

What is claimed is:

1. In a low pressure are discharge lamp of the fluorescent type the combination comprising a light transmissive envelope of generally tubular shape having an ionizable gaseous medium therein, a pair of light transmissive plates mounted in a predetermined spaced relationship within said envelope to form'a predetermined non-circular crosssectional area bounded by the opposing forces of said plates and the adjacent portions of the envelope inner wall therebetween, and means spaced in said envelope for establishing an arc discharge therebetween and thereby forming an arc-stream within said envelope, said arcstream being confined between said plates in the said crosssectioual area to control the path and the cross-section of the arc-stream.

2. An electric discharge lamp as set forth in claim 1 wherein in said plates are bowed in toward each other to form a non-circular cross-section of generally hour glass shape.

3. An electric discharge lamp as set forth in claim 1 wherein said spaced plates are flat and extend along the axis of the envelope.

4. An electric discharge lamp as set forth in claim 1 wherein said spaced plates are formed in the shape of a helix and extend along substantially the entire length of the envelope thereby causing said arc-stream to travel in a helical path.

5. An electric discharge lamp as set forth in claim 1 wherein each of said plates extends along the axis of the envelope and also has portions thereof extending toward said other plate thereby causing said arc-stream to also travel in a path lateral to the axis of the envelope.

6. An electric discharge lamp as set forth in claim 1 wherein each of said plates extends along the axis of the envelope and also has portions thereof extending toward said other plate, an extending portion of one of said plates arranged to lie between two extending portions of the other plate, thereby causing said arc-stream to travel in a Wavelike path with a deflection lateral to the axis of said envelope.

7. An electric discharge lamp as set forth in claim 6 wherein said plates are also formed in the shape of a helix thereby causing said arc-stream to travel in a helical path as it moves in the wavelike path between the plates.

8. An electric discharge lamp as set forth in claim 6 wherein said extending portions are substantially arcuate in shape.

9. An electric discharge lamp as set forth in claim 6 wherein said extending portions are substantially flat and are extended from said plates by walls which are substan tially vertical to the plates and the extending portion.

10. An electric discharge lamp as set forth in claim 1 wherein said spaced plates are fiat and extend along the axis of the envelope.

11. An electric discharge lamp as set forth in claim 1 wherein said spaced plates are formed in the shape of a helix and extend along substantially the entire length of the envelope thereby causing said arc-stream to travel in a helical path.

12. An electric discharge lamp as set forth in claim 1 wherein each of said plates extends along the axis of the envelope and also has portions thereof extending toward said other plate thereby causing said arc-stream to also travel in a path lateral to the axis of the envelope.

13. An electric discharge lamp as set forth in claim 1 wherein each of said plates extends along the axis of the envelope and also has portions thereof extending toward said other plate, an extending portion of one of said plates arranged to lie between two extending portions of the other plate, thereby causing said arc-stream to travel in a wavelike path with a deflection lateral to the axis of said envelope.

14. An electric discharge lamp set forth in claim 13 wherein said plates are also formed in the shape of a helix thereby causing said are-stream to travel in a helical path as it moves in the wavelike path between the plates.

15. An electric discharge lamp as set forth in claim 13 wherein said extending portions are substantially arcuate in shape.

16. An electric discharge lamp as set forth in claim 13 wherein said extending portions are substantially fiat and are extended from said plates by walls which are substantially vertical to the plates and the extending portion.

17. In a low pressure arc discharge lamp of the fluorescent type the combination comprising a light-transmissive envelope of vitreous material of generally tubular shape having an ionizable gaseous medium sealed therein, a pair of plates of light transmissive material mounted in a predetermined spaced relationship within said envelope to form a predetermined non-circular cross-sectional area which is bounded by the opposing faces of said plates and the adjacent inner wall portions of the envelope therebetween, means spaced at the ends of said envelope for establishing an arc discharge in said envelope therebetween thereby forming an arc-stream within said envelope, said arc-stream being confined between said plates in the said cross-sectional area to control the path and the cross-section of the arc-stream, and a phosphor coating on the opposing faces of said plates and on the portions of inner wall of the envelope therebetween for reacting with said arc-stream to produce visible light, said light being transmitted through said plates and said envelope.

18. An electric discharge lamp as set forth in claim 17 wherein said plates are bowed in toward each other to form a non-circular cross-section of generally hour 7 glass shape.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 l21,l83 February 11, 1964 Carl E0 Swanson e above numbered patthat error appears in th uld read as It is hereby certified ent requiring correction and that the said Letters Patent sho corrected below Column 6 lines 55 58, 63 and 68. for the claim reference numeral 1" each occurrence, read 17 =-=-a Signed and sealed this 23rd day of June 1964,

(SEAL) Attest:

EDWARD J BRENNER ERNEIST W. SWIDER Attestmg Offlcer Commissioner of Patents 

1. IN A LOW PRESSURE ARC DISCHARGE LAMP OF THE FLUORESCENT TYPE THE COMBINATION COMPRISING A LIGHT TRANSMISSIVE ENVELOPE OF GENERALLY TUBULAR SHAPE HAVING AN IONIZABLE GASEOUS MEDIUM THEREIN, A PAIR OF LIGHT TRANSMISSIVE PLATES MOUNTED IN A PREDETERMINED SPACED RELATIONSHIP WITHIN SAID ENVELOPE TO FORM A PREDETERMINED NON-CIRCULAR CROSSSECTIONAL AREA BOUNDED BY THE OPPOSING FORCES OF SAID PLATES AND THE ADJACENT PORTIONS OF THE ENVELOPE INNER WALL THEREBETWEEN, AND MEANS SPACED IN SAID ENVELOPE FOR ESTABLISHING AN ARC DISCHARGE THEREBETWEEN AND THEREBY FORMING AN ARC-STREAM WITHIN SAID ENVELOPE, SAID ARCSTREAM BEING CONFINED BETWEEN SAID PLATES IN THE SAID CROSSSECTIONAL AREA TO CONTROL THE PATH AND THE CROSS-SECTION OF THE ARC-STREAM. 